A radial rake angle is the angle formed by a reference plane at the face of the cutting insert measured to a plane which originates at the center origin of the body and ends at the sharp corner of the cutting insert. An axial rake angle is the angle formed by the reference plane of the face of the cutting insert measured to a plane parallel to the axis of the cutting body at the cutting point. The reference plane is a plane described by the cutter centerline. In brief, a positive rake angle is achieved when the cutting insert is positioned behind a line passing through the center of the cutter. Conversely, a negative rake angle cutting insert is positioned ahead of the center line of the cutter.
Positive rake angle cutting inserts are desirable because the cutting edge has a shearing effect on the workpiece and are especially desirable for machining high temperature alloys and non-ferrous materials having a high modulus of elasticity (e.g., aluminum). In addition, positive rake inserts exert less force on the workpiece during machining.
In circular or milling cutters, the use of positive rake angle is limited because of the lack of heel clearance. Heel clearance is measured as the angle formed by the top of the cutting insert and a perpendicular line connecting a first plane passing through the center of the tool body and the top rear of the cutting insert and a second plane, parallel to the first plane, which passes through the cutting edge.
Insufficient heel clearance results in interference between the rearward, non-cutting surface of the insert and the workpiece. Due to this problem, cutting inserts are often positioned ahead of the center line of the milling cutter to obtain sufficient heel clearance. This, however, results in a negative rake angle. Negative rake angle cutting inserts exert a pushing action on the workpiece and thereby exert more force on the workpiece and have a tendency to deform the workpiece leading to less precise cuts.
It is therefore an object of the present invention to provide a cutting tool containing at least one cutting insert which has the combination of a positive rake angle and sufficient heel clearance.
It is a further object of the invention to provide a cutting insert with at least one prismatic face having a positive rake angle and sufficient heel clearance for use in a milling cutter.
It is a still further object of the invention to provide a wedge and locator seat used in combination with the cutting insert for positioning and securing the cutting insert of the invention in a milling cutter.